Polyurethane coated fabrics are used in a wide array of products and applications, including high performance applications such as fuel cell fabrication for aviation fuel containment, and as automobile passive restraint systems, specifically air bags.
The air bag is preferably assembled from a urethane coated fabric that can be heat sealed. The fabric is a laminated product. The fabric is dipped in a urethane adhesive and then the urethane film laminate is placed on the adhesive. This produces a low cost, lightweight coated fabric that can be fabricated by methods including heat bonding and dielectrical welding, into an automotive restraint device that will remain inflated to protect the vehicle occupants form injury during a side impact of rollover accident.
High performance polyurethane elastomers include, for example, polytetramethylene glycol (polyether) polyurethanes and poly(butane adipates or hexane adipates) ester polyurethanes. The polyether polyurethanes exhibit good hydrolytic stability and good low temperature properties but offer typically poor oxidation resistance. The polyester polyurethanes, on the other hand, exhibit good toughness, abrasion resistance, and oxidation resistance, but are less resistant to hydrolysis. Polyurethanes based on polycarbonate polyols are known to have good hydrolytic stability and generally have good resistance to other degradation forces; however, these polyurethanes are typically too hard, rigid and brittle for use in industrial fabrics.
High performance coated fabrics are based primarily on the polyester polyurethanes, based on their overall performance, despite their relatively poor hydrolytic stability.
U.S. Pat. No. 5,298,303 is directed to a coated fabric for use as an automobile air bag that can accommodate rapid inflation and maintain an internal pressure for a period of time. The fabric comprises a fibrous skeleton that is coated with a plurality of layers wherein at least one of the coating layers comprises a polycarbonate-polyether polyurethane formed from a polyol. A second layer comprises a second polymer such as polyurethane or an elastomer. At least a portion of the structure may include, as an initial layer, an adhesion aid to assist in the bonding of the coating layers. The adhesion aid is preferentially an aziridine compound.
U.S. Pat. No. 5,302,432, directed to an automobile air bag, discloses a fabric comprising a woven synthetic fiber, a film of a polyolefin group resin laminated on a side of the woven fiber, and a non-woven fabric laminated on the film. Preferably, the woven fabric is manufactured by weaving a multi-filament of a polyamide group or a multi-filament of a polyester group. A polyamide fiber, a polyester fiber, or a regenerated cellulose fiber can be used for the non-woven fabric. During manufacture, both the woven and non-woven fabrics are closely bonded to a molten portion of the resin film, which solidifies upon cooling to form a low air permeability composite fabric.
U.S. Pat. No. 5,407,728 is directed to a fabric containing a graft polymer to be used for an air bag substrate capable of maintaining the integrity of the sewn seams during packaging, compaction, and inflation. The method of making the fabric involves contacting fibers and yarns with a grafting solution at any stage of production. Thus, the grafting solution may be applied to filament fibers, yarns, or formed fabric either before or after chemical or mechanical production operations such as spin finishing, application of lubricants, or sizing. The grafted air bag fabric has a reduced fabric porosity and increased structural integrity. The method utilizes a grafting solution containing water, a catalyst for activating or regenerating a graft initiator in the presence of the fibers or yarns, a graft initiator, and at least one component, such as a water dispersible polyurethane polymer, having a functional group that reacts with and bonds to the fibers or yarns. The grafting solution may also contain second component, such as a monomer, that covalently bonds to the first component or bonds directly to the fibers or yarns. The method includes the general sequence of radical formation; initiation and extension, where the free radical reacts with the first or second components; propagation; and termination.
U.S. Pat. No. 6,183,009 relates to a multilayered textile composite material for use in an inflatable gas bag that comprises at least one layer of a textile material and one layer of a polymer material whose melting range is lower that the melting range of the textile material. The textile composite material is formed into a specified three-dimensional shape which is to develop during inflation of the gas bag, and the individual layers of the textile composite material are joined together in this three-dimensional shape so as to avoid the formation of creases in the inflated state.
In the manufacture of fabrics for use in automobile air bags, for example, the fabric must be low cost, light weight, and fire retardant. Furthermore, the fabric must be both of sufficient strength to resist instant expansion and possess the ability to be folded compactly.
A method of adhering a preformed elastomer film to a fabric material by using an adhesive is known. This method is generally unsuited to the manufacture of composite fabrics for use in automobile air bags, however, because the adhesive percolates between filaments in the fabric producing a laminated cloth that is undesirably hard and stiff. Furthermore, the conventional method produces a fabric with imbedded adhesive and thus yields a flammable laminated cloth, which is incompatible with federal motor vehicle safety standards.
Accordingly, there is a need for a composite fabric suitable for use in an automobile airbag comprising a thermoplastic film laminated via an adhesive to a fabric core and a method for making the same.